kmno4
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Simple preparation of chloroacetone - an essay
This is relatively simple synthesis, but rather for slightly more advanced mad-experimenters.
WARNING ! : Unhealthy properities of chloroacetone are commonly known, if not, then find and read a MSDS for this compound. Any
prolonged contact with its vapours will cause adsorpion on you clothes, skin and hair and further slow desorption, causing long-lasting (hours), not
very pleasant eyes pain. You have been warned !
In order to conduct some other exeperiments, small amount of chloroacetone was needed.
The literature gives several methods of its synthesis, but none is free form some experimental shortcomings.My goal was to do this as simple and safe
as possible, without using gaseous Cl2 and generatinng useless HCl... etc.
The idea looks like this:
CH3(CO)CH2-H + HCl + [O] → CH3(CO)CH2-Cl + H2O + inorganic salts, where [O] marks some oxidizer.
Of course, the idea is nothing new, but I did not found any good-looking procedure utillizing such reaction.
As the most suitable oxidizer for this purpose, KMnO4 was chosen. It is because of its availability and high differece between oxidation states of
Mn(II) and Mn(VII). Instead of HCl(aq), the mixture of NaCl and H2SO4 was used (just larger amount of old H2SO4 was at hand).
Total reaction:
CH3(CO)CH2-H + KMnO4 + NaCl + H2SO4 → CH3(CO)CH2-Cl + MnSO4 + NaHSO4 + KHSO4 + H2O
(balancing the equation is left for interested).
About 100% excess of acetone was used, in order to reduce polychlorination reactions.
Sample preparation is described below.
In 200-300 cm3 conical flask, with glass stopper, on magnetic stirrer, 26 g of NaCl with 30 g of H2O is placed, then 20 g of acetone is added. The
content is stirred shortly (manually) and the flask is placed in larger vessel filled with r.t. water. The rection is performed in temperatures not
exceeding ~30-35 C, to avoid using additional glass equipment, so such themostating water bath is desired, however not necessary (especially on
smaller scale experiments).
In separate beaker, solution of 39 g of conc. H2SO4 in 25 g of H2O is prepared (if ice is used, no cooling is needed). 12,8 g of KMnO4 is weighed -
this is limiting reagent and corresponds to 11,6 g of acetone to be monochlorinated, but it is only theory, commercial KMnO4 is never of 100% purity
and chlorination 100% selective to monochloroderivative.
Stirring is started, about 1/4-1/3 of prepared H2SO4 solution is added and small (0,2-0,3 g) amount of (crystalline) KMnO4 is added. The flask is then
stopperded. The mixture becomes violet, but it soon (a minute or so) turns to deeply brown colour (unstable Mn(IV)/Mn(III) chloride salts).After few
minutes the colour fades and all becomes coloreless. Another small portion of KMnO4 is added, the violet quickly dissapears giving "browns". In this
way, chlorine is generated in situ and consumed by acetone.
VERY IMPORTANT ! KMnO4 must be added in small portions (minimum 15 ones). Another portion can be added when the liquid mixture
becomes colorless (or almost colorless) after additiom of earlier portion of KMnO4.
If added too much or too quickly, some gaseous chlorine is formed, generating pressure inside the flask and the stopcock can be pushed out. In general
it is not vary harmful for the reaction, but it generates lachrymatory fumes, containing Cl2 - not very interesting mixture to breathe in.
Under these conditions (~r.t.), the reaction is slow and requires about 4-5 hours to complete. After several added portions of KMnO4, additional
amount of H2SO4 solution is added to keep the reaction mixture strongly acidic. When ~50% of total KMnO4 was added, the rest of H2SO4 should be added.
As reaction goes on, it becomes slower and slower, last portions of oxidizer dissapear during many minutes. In prelimenary experiments, it was checked
that too small amount of acid causes very long time of consumption of last portions of KMnO4 (after 24 hours my patience was exhausted). When reaction
is completed, the flask contains slightly pinkish, tansparent water phase (lower) and almost colorless organic phase (upper).
It was carefully pipeted out and weighed. Several runs were made (on scale as above) and every time the amount was practically the same: 21,8 g.
Reaction conducted on 1/2 scale gave also 1/2 of that amount.
Post-reaction water layer is strongly lachrymatory and in one run, additional extraction with DCM was tried.
The water layer was cooled to ~10 C and 3.0 g of DCM was added and stirred for some time. Next, the DCM layer (lower) was pipeted out and weighed: 4,1
g. Second portion (3,0 g) of DCM was added, and so on..., and weighed: 3,1 g. As can be seen, only small amount of organics are extracted from acid
water layer, at least with DCM, and in further runs only organic layer from post-raction mixtures was collected.
The organic layer was placed in a bottle (flask, whatever) and ~0,2 g of CaCO3 (precipitated, not chalk-like crap grade) was added to remove all acid
substances. When water-layer was not perfectly separated, CaCO3 will attain pink coloration - it is just MnCO3. After several hours CaCO3 was removed
(must be powdery, if not then CaCO3 treatment should be repeated), washed with small amount of acetone, all liquids combined and dried with MgSO4.
Very weak caking takes place, so water content in the organic liquid is low.
After drying, the liquid is ready for distillation. If someone has no time for it, another portion of CaCO3 (0,1 g or so) should be added to the
liquid, then it can be stored for some longer time (best in brown glass bottle, storing temp. lower than 20 C). After ~7 days no traces of
decomposition was (visibly) detected, the color of the liquid does not change at all.
Slightly more than ~60 cm3 of the liquid (from few runs) was placed in 100 cm3 RBF and distilled under normal pressure. Most of unreacted acetone
comes in 56 C - 90 C range, then distillation slowes down.
Heating is slightly increased, more distillate starts to collect starting from ~115 C. It is mainly chloroacetone (and possibly 1,1 dichloroacetone).
Further, the boiling temperature practically stops at 120 C.More than 90% of distillate is collected in range 116C - 124 C (overheating in the
RBF-head in the end of distillation). Unfortunately not everything is OK. When practically all acetone is removed and temperature inside RBF starts
rising above 100 C, the color of liquid inside quickly changes from pale yellow, through brown to carbon black. It is commonly known as "black death"
- indeed, very adequate name.
The amount of chloroacetone distillate corresponds to ~70 % of KMnO4 used. When cooled RBF was disjoined from the head, it turned out that all
apparatus is filled with HCl fumes.
It is very probable that decomposition of chloroacetones into such carbonaceous material is autocatalytic process, with HCl acting as catalyst.
To the prepared distillate ~0,3 g of CaCO3 was added, botteled and set aside. In the meantime, additional synthesis was performed (with 20 g of
acetone). Prepared liquid (treated with CaCO3/MgSO4) was mixed with that distillate, placed in 100 cm3 RBF, ~0,5 g of CaCO3 was added and set for
distillation. Added carbonate made a little wonder during distillation- practically no "black death" is formed !
Small amount of carbon-like material was collecting on the walls of RBF above the liquid, but is the cause of not very proper heating (100 cm3 RBF in
250 cm3 mantle). Practically to the very end of distillation the suspension inside the flask was bright. When temperature in the head reached 135 C
(larger overheating, very small amount of liquid left inside the RBF, about 1-2 cm3), the distillation was stopped. It looks much better than
distillation without CaCO3, larger amount of chloroacetone is recovered and no HCl was detected.
Few attempts were made to check somehow purity of prepared chloroacetone, at least by determination of chloride content. Unfortunalety, it turns out
not so easy. Any direct methods (AgNO3 titration, NaOH titration also in "back" version) failed. It is because the product(s) of chloroacetone
hydrolysis (in water) possess reducing properities and such hydrolysed solution has coloration changing as pH changes.
The only reasonable way to Cl estimation leads via chloroacetone hydrolysis, evaporating obtained solution to dryness and ignating the residue to
remove all organic carbon. I am going to do this in near future, in this moment my AgNO3 is almost out and the demi-water I have becomes turbid when
AgNO3 is added.
Density of prepared chloroacetone was measured: 1,143 g/cm3 at ~20 C and 1,151 g/cm3 at ~14 C.
It is important to realize that (single) simple distillation (as above) does not remove completely low- and high- boiling impurities (e.g. acetone,
mesityl oxide, dichloroacetones.... etc). So even correct Cl content and literature density is not any proof of purity*. Only GC would judge something
Remarks.
To prepare purer chloroacetone, with better yield, more acetone should be used, for example* 30 g instead of 20 g. The destilled off acetone fraction
can be reused in subsequent preparation (as I did).
The chlorination reaction goes via "MnO2" formation and reduction, added KMnO4 oxidize (in very fast rate) Mn(II) to this "MnO2", but under these
conditions it is rather MnO(OH)2. Lower temperature of the reaction was also chosen to minimalize side reactions - organic oxidations and
condensations. The reaction was also tried with commercial steel-black MnO2, but it is almost inert under the reaction conditions. When MnO(OH)2 was
used (brown powder, prepared from MnSO4 and KMnO4), the reaction goes smoothly.
Also KClO3 was tested as oxidant and it indeed works. At high Cl(-) concentration, in acidic media, chlorate decomposes mainly to Cl2 and there are
chlorination reactions based on chlorates, described in chemical literature.
Unfortunately, organic layer separating during the reaction has very suspiciously yellow color, I am almost sure that it is ClO2 extracted to organic
layer. As potentially very dangerous mixture to distill, the idea was abandoned. I have found "chlorine generator" description, where Cl2+ClO2 mixture
is generated from KClO3 and HCl(aq), ClO2 is then removed by Mn(II) salts solution (in separate vessel). Maybe small amount of Mn(II) would act as
ClO2 remover ( ClO2+Mn(II) → Cl(-) [or Cl2] + MnO(OH)2 ) also in chlorinating solution, but it was not investigated. KClO3 methode is very
convenient for preparing bromoderivatives, because Br(-) is much better reductor than Cl(-). One must be careful, because chloroacetone is onion-like
toy comparing to, for example, bromoacetophenone.
It is known that chloroacetone gives nice crimson coloration with bases (NaOH, KOH) in water. But it seems that it is rather caused by some products
of chloroacetone decomposition (hydrolysis, condensation ?). During relatively short period (single hours) chloroacetone is completely hydrolyzed, but
the coloration is stable (at least for days). Some rather not pleasant odour is present in such mixture, reminding me isobutanol or n-propanol (acetol
?). When the solution is acidified, the color changes to orange, basified back it becomes crimson again. The orange mixture has different odour,
reminding me xylene. Maybe it is not caused by monochloroacetone at all, but by some impurities ?Interesting...
* see DOI: 10.1021/ja01219a013, referenced as <189> in here, in chloroacetone compound section
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Boffis
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@kmno4, great write up and an interesting modification to the chlorination of acetone. I have often contemplated preparing chloroacetone but shied
away. I'll have to give your method a go! I was interested in preparing 2-amino-4-methyl-thiazole from the reaction between chloroacetone and
thiourea. I was interested in your observation that the addition of calcium carbonate to the organic phase before distillation had a positive effect
on the distilled yield and the carbonized by-products.
I also liked your tests of other oxidizing agents, particularly chlorate. I have used chlorate / hydrochloric acid for the chlorination of caffeine
and its oxidation to dimethyl alloxan. I doubt that chlorine dioxide accumulation would be a problem over a prolonged reaction time.
Great link to the the Huntress book! I have a hard copy already but it good to see that a digital copy is available as the original is hard to find
now.
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kmno4
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Quote: Originally posted by Boffis  | | I was interested in preparing 2-amino-4-methyl-thiazole from the reaction between chloroacetone and thiourea. |
I have tried this, for fun, with 2,0 g of prepared chloroacetone + 1,86 g of thiourea + 11 cm3 of methanol in small flask. The mixture is transparent
and colorless, nothing seems to happen. But when the flask was warmed in my hand, the content was getting warmer than my hand and when set aside, it
remained warm for some longer time. After 1 hour, one droplet of the solution was placed on watch glass and evaporated. No chloroacetone was detected,
the reminder rubbed with glass rod turns to white powder (sharp, short lasting salty taste). It is one of the most banal preparations I ever made 
[Edited on 21-4-2021 by kmno4]
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